The use of silicon-on-insulator (“SOI”) transistors in integrated circuits is continuously increasing due to their high performance and low power consumption. As such, accurate modeling of SOI transistor behavior is becoming increasingly important for precise circuit simulations for designs utilizing SOI transistors. In particular, the floating body structure of SOI transistors have made the need for accurate SOI transistor body-effect models of critical importance.
However, using conventional SOI transistor test structures presents difficulties in making accurate measurements of the body-effect in SOI transistors. For example, one type of conventional SOI transistor test structure includes a semiconductor body having a doped halo region situated adjacent to a semiconductor body tie region. A gate is situated over the doped halo region of the semiconductor body and over a portion of the semiconductor body tie region. A heavily doped semiconductor body contact is situated within a portion of the semiconductor body tie region that extends beyond the gate, and a lightly doped semiconductor body portion is situated between the heavily doped semiconductor body contact and the doped halo.
To measure the body-effect using the conventional SOI transistor test structure, the voltage at the doped halo is varied by applying a voltage to the semiconductor body contact and the threshold voltage of the transistor is measured to determine the body-effect. However, since the heavily doped semiconductor body contact has substantially greater doping than the lightly doped semiconductor body portion, current flow between the heavily doped semiconductor body contact and the doped halo region of the semiconductor body can be impeded by a depletion region that can form in the lightly doped semiconductor body portion. As such, the voltage of the doped halo can differ significantly from the voltage applied to the heavily doped semiconductor body contact, resulting in erroneous threshold voltage measurements and inaccurate body-effect models.